Can you keep an app free and private for tests and later switch it to paid and public?

[Mrch]

I seem to understand that you can't switch from free app to paid app.

But the developer bridge often lags and it's much better to upload the app as private link and update the app until you have a working product you are ready to sell.

Will this be allowed?

Do I need to create an entirely new watchface for this to work?

Or as long as it's not free and public, I'm fine?

[JonHagen]

Unfortunately, like you suggest- there's no way to promote the app once you've designated it as 'free'. 

You'll have to create a new project (with a new UUID that will be generated for you) in order to sell it.

I haven't tried building a paid app, but I believe you can create the paid project, and that private link will be 'free' to those with the link.